The invention relates to a regeneration and life-prolonging process of an etching solution that uses an alkaline permanganate etching solution or a waste liquid thereof and a unit therefor, in particular, a process of applying a batch process to an alkaline permanganate solution or a waste liquid thereof to regenerate and prolong a lifetime and a unit therefor. Furthermore, the invention relates to a regeneration process of an alkaline permanganate etching solution that uses an alkaline earth hydroxide such as calcium hydroxide and simultaneously relates to a process that generates and uses an alkaline metal compound such as sodium hydroxide necessary for an alkaline permanganate solution.
So far, an alkaline permanganate etching solution has been applied to an etching process of a resin such as a desmear process or a roughening process of a wiring board. In general, when a throughhole disposed on a wiring board is plated to establish electrical continuity, a cutting debris such as a resin that disturbs the electrical continuity after a throughhole is formed remains. The desmear process is a process by which decomposes a resin component in an alkaline permanganate etching solution. Furthermore, the roughening process is a process by which a surface of a resinous insulating layer is roughened with an alkaline permanganate etching solution.
Recently, an additive process where a resin is coated on a surface of an inner layer board, the resin is directly plated, and a pattern etching is applied thereto to prepare a wiring board is being adopted. In the additive process, in order to improve the adhesiveness between the resinous insulating layer and the plating, before applying a plating process, a surface of an insulating layer is roughened. In an etching process of a resin, which uses an alkaline permanganate etching solution, in the alkaline permanganate etching solution, carbon (C) of a resin component and a hydroxyl group (OH−) in the alkaline solution react with permanganic acid as shown by an equation (1) below to decompose the resin component.
[Formula 1]4MnO4−+4OH−+C (organic resin component and the like)→4MnO42−+CO2+2H2O  (1)
However, in the existing technology mentioned above, when the alkaline permanganate etching solution is kept on using, carbon dioxide (CO2) generated from carbon (C) in the resin and carbon dioxide present in air are taken in the liquid to react as shown by an equation (2) to increase carbonate ions in the liquid.
[Formula 2]CO2+2OH−→CO32−+H2O  (2)
As the result, carbonate ions are accumulated in the etching solution. On the other hand, a concentration of hydroxyl groups (OH−) necessary for etching is lowered. When the carbonate ions are accumulated in the etching solution, the lifetime of the etching solution becomes shorter. Furthermore, when the hydroxyl group ions in the etching solution are lowered, the etching capability is lowered. Still furthermore, the alkalinity of the etching solution is managed by the neutralization titration. However, since, in the neutralization titration, not only the hydroxyl group ions but also carbonate ions (CO32−) are neutralized, accurate alkalinity cannot be analyzed to deteriorate the accuracy in the liquid analysis. Thus, when a carbonate ion concentration in the alkaline permanganate etching solution increases, there is caused a problem in that the etching efficiency is deteriorated and an accurate hydroxyl group concentration can be analyzed with difficulty.
In the etching process that uses an alkaline permanganate etching solution, as the background arts relating to regeneration of the etching solution, what follows can be cited.
In patent literature 1 (JP-A No. 06-6033), a process where the stability of an etching bath can be maintained, etching defects are inhibited from occurring and a constant etching speed can be maintained is proposed. According to the proposal, a predetermined amount of an etching solution is sampled at a predetermined time interval from the etching bath, concentrations of permanganate, sodium hydroxide and manganate are analyzed by use of an automatic analyzer, the analysis values are calculated by a controller, and a replenishment amount for controlling the sodium hydroxide concentration to a predetermined concentration is transferred to a quantitative pump of sodium hydroxide. Furthermore, a predetermined amount of the etching solution is sampled at a constant time interval in an etching rate measuring cell, an organic solvent in the same system as that of a processed matter is kept on dripping by a circulating pump until the solution color of a calorimeter changes from red purple to green, and thereby the etching rate in the etching bath is managed while sustaining the concentration of the permanganate in the etching solution within a constant range.
Patent literature 2 (JP-A No. 2000-13000) relates to an etching process of a resin indispensable for a high-density print circuit board. In the etching process, when, in order to precipitate with a particular treatment solution carbonate ions accumulated as a reaction product in a solution and remove to stabilize the etching solution and prolong a lifetime thereof, when an alkaline permanganate solution in an etching bath is circulated by a pump, a specific solution is injected in the middle of a piping, carbonate that is a reaction product is precipitated and filtrated with a filter to remove, the alkalinity is measured with an automatic analyzer to adjust to a predetermined normality, and with the solution the resin is etched.
In patent literature 3 (JP-A No. 2001-156428), in an etching process that uses an alkaline permanganate etching solution, a method of improving the etching efficiency is proposed. According to this, in an etching bath, an alkaline permanganate etching solution is accommodated and in the etching bath an etching agent to be etched is etched. In a reaction chamber, barium chloride is added from an additive tank to react with carbonate ions to form barium carbonate that is a hardly soluble salt. Barium carbonate can be separated from an ion component by use of an ultrafilter.
[Patent literature 1] JP-A No. 06-6033
[Patent literature 2] JP-A No. 2000-13000
[Patent literature 3] JP-A No. 2001-156428
In the regeneration methods of an etching solution due To the background art literatures, patent literature 1 relates to an etching process that uses an alkaline permanganate etching solution. In the regeneration method, continuous steps such as concentration analysis, calculation with a controller and a measurement of the etching rate are necessary, that is, a complicated process is necessary to manage and process the etching solution.
Patent literature 2 is same as the patent literature 1 in a point that an alkaline permanganate etching solution is used to etch. However, the process is continuously carried out and a barium compound such as barium chloride is fundamentally used.
In patent literature 3, similarly to the above, an alkaline permanganate etching solution is used to etch. The processing is continuously carried out, an ultrafilter is used, and fundamentally barium carbonate is used.
In this connection, the invention intends to provide a regeneration process of an alkaline permanganate etching solution, which, in an etching step that uses an alkaline permanganate etching solution, in order to inhibit the etching efficiency from deteriorating, can simply and efficiently regenerate an etching solution to prolong a lifetime thereof and a unit therefor and to reduce a harmful waste solution.